Enduro Directline 12T SRAM 12sp Road & Gravel XD15 GraphiteXD 15 Ceramic bearings provide superior smoothness, reduced weight and extended bearing life A CN (tight clearance) upper pulley bearing maximizes shifting accuracy while a C4 (loose clearance) lower pulley bearing promotes unconstrained chain line movement AB0030: 12 tooth pulley set with 4mm upper & 5mm lower bolt holes is designed as direct fit upgrade for SRAM 12 speed road and gravel derailleurs AB0031: The eleven tooth upper and twelve tooth